The present invention relates to a procedure for feeding of powder-like substances to a discharging means and in particular to feeding of powder-like substance onto a flat product as, for example, a sheet of paper and a device for performing this procedure.
The present invention will be described in the following using the example of a powder duster for a printing machine. It must be pointed out that this procedure and device is also suitable for the feeding of powder-like substances in other technical fields and that the description of the invention with respect to a printing machine does not in any way signify a restriction of the application of the present invention.
To further simplify, the printed products are designated as sheets; this fact as well shall not signify a restriction and encompasses all types of printable products and objects.
In printing machines of the type referred to here, printed sheets are conveyed at relatively high speed onto a stack. At output speeds of 2 to 3 sheets per second and higher, the danger exists that the printed color may not have completely dried before the next sheet is conveyed onto the stack. When this happens, some of the printed color adheres to the reverse side of the next sheet, resulting thereby in an unusable product. In order to avoid such circumstances, the printed surfaces are dusted with powder by means of a powder dusting device. The powder employed prevents the adhering of a successive sheet to the previous sheet.
A powder duster having a powder receptacle arranged at its top is known from U.S. Pat. No. 5,615,830. The bottom of said powder receptacle has an opening under which a transporting drum or a conveyer belt disposed with cavities is provided for the receipt and transport of powder. Received powder is conveyed into a separate chamber in which an air feed and an air discharge outlet is provided. The powder swirled up by means of the horizontal air feed is then conveyed further through the likewise horizontal air discharge outlet.
The discharging of the powder onto the paper must transpire with high precision. Should too little powder be introduced, the desired effect will not be achieved and the printed product will be unusable.
Should too much powder be introduced, an undesirable high consumption of the material ensues as well as the danger arising that the powder will be applied unevenly. Should an uneven introduction of powder occur on a plurality of identical sheets, one end of the stack will end up higher than the other end and will slide off.
The operators of such printing machines expect that their operation will transpire automatically and largely without need for control over a period of several hours. The powder feeding means must therefore be so configured that it will function reliably without malfunction.
Powder atomizers are typical auxiliary devices for printing machines. For the buyer, the cost of such an accessory device must be in an acceptable ratio to the end price of the machine, so that the buyer""s available financial resources, in particular with reasonably priced printing machines, is very limited.
Taking the above-mentioned considerations as a starting point, it is therefore the task of the present invention to provide a procedure and a device for feeding of powder to a powder discharging means which is reliable and which will function flawlessly over a longer period of time and which can nevertheless be manufactured at reasonable cost.
The procedure according to the present invention, the inventive device respectively, is configured in such a manner that a powder receptacle is provided connected to a vacuum means. A partitioning means is arranged within the powder receptacle for separating a portion of the powder from the remaining quantity of powder in said receptacle.
An air outlet device is arranged such that it feeds air to the separated quantity of powder in such a manner that the powder is swirled upwards by this emitted air.
The vacuum means simultaneously generates a vacuum effective within the powder receptacle which induces the air with the swirling powder to be sucked up and fed to the discharging means through suitable conduits, etc.
The inventive configuration of the procedure and device has considerable advantages compared to the state of the art.
Machine operators want to have as large of a powder reserve as possible at their disposal. A large reserve of powder however necessitates a correspondingly large reserve container. Since the quantity of powder within the powder receptacle changes during operation, the flow ratio also changes, whereby the amount of the swirled up powder and thereby the powder concentration changes in the siphoned-off air flow. In contrast thereto, the partitioning of a quantity of powder from the total quantity induces that the air flow effects only a small portion of the powder quantity and that thereby the swirled up quantity is no longer, or only in small measure, dependent upon the fill capacity of the powder in the powder receptacle.
In accordance with a preferred embodiment, the powder receptacle is arranged essentially perpendicular, whereby the air siphoning device is then preferably disposed above the receptacle.
The partitioning means preferably constitutes a chamber which, with a vertically disposed powder receptacle, is open, at least partially, at its upper end and at its bottom end.
The powder receptacle is preferably configured rotation symmetrical whereby the axis of rotation is essentially perpendicular and the chamber is then preferably likewise configured such that its longitudinal axis coincides with said rotational axis.
The chamber is likewise preferably configured rotation symmetrical whereby then both the rotation symmetrical axes of receptacle and chamber coincide with one another.
The chamber is preferably configured in cyclone or funnel or tapered shape; i.e. its extension in cross-section, meaning as seen horizontally, diminishes downwardly.
The air feed device is preferably aligned with respect to the partitioning means, respectively the chamber wall which it forms, such that the air flow initially impacts the chamber wall before being deflected from this point onto the powder.
In accordance with a preferred embodiment of the present invention, should such a need arise, for a device configured without the powder receptacle having a partitioning means, the device according to the present invention further comprises a refilling means.
When conventional powder receptacles have to be refilled, the powder receptacle must be removed, filled with powder and then put back on. The running of the corresponding machine must of course be stopped during the time this process takes.
In the powder receptacle of the embodiment according to the present invention described herewithin, a reserve container is provided above the powder receptacle and is joined thereto by means of a corresponding locking means, preferably a locking valve.
Opening the valve allows powder to fill into the powder receptacle from the reserve container without the need for interrupting the operation of the machine.
In the present description, the formulation of the patent claims and in the following description, it is to be assumed that the matter to be conveyed is a powder and that the conveying medium is air. It is to be noted that the invention may also be applied with other matter to be conveyed which is perhaps not normally characterized as being of powder form, provided that the behavior of said matter in a flowing medium is similar to the herein described behavior of powder.
Furthermore. the transport medium is not solely limited to air. According to demand, another gas may be used, for example nitrogen, helium or other such gasses.
Especially preferable, however, is the utilization of the invention with powder which is suitable for dusting of newly printed products, powder such as calcium carbonate, for example, and which has a grain size between 5 and 100 xcexcm, especially preferred between 15 and 50 xcexcm.
Further advantages, characteristics and possible applications of the present invention will now be described in the following with respect to an embodiment and in reference to the drawing figures.